1. Field of the Invention
The present invention relates to a lighting failure detector for a luminaire, and more particularly to a detector for ascertaining that a lamp, such as a street lamp, is automatically lit at night and indicating a failure if any.
2. Description of the Prior Art
A lamp, such as a street lamp capable of automatically lighting in the dark is not lit during the daytime, and a daytime inspecting patrol cannot ascertain whether or not the particular lamps were lit at night.
In order to overcome the inconvenience encountered by the daytime inspecting patrol, there is a proposal which is disclosed in Japanese Patent Kokai No. 2-60092 which shows a lighting failure detector for a luminaire which indicates an occurrence of any lighting failure at night and retains it until daytime.
This known lighting failure detector uses a photocell for detecting the illuminance of the lamp and natural illuminance in daytime, and an indicator functioning as a memory. It is operated as follows:
When night falls and the lamp is automatically lit, the photocell does not operate the indicator by detecting the illuminance of the lamp. However, if the lamp is not lit, the photocell detects a decrease in natural light, and operates the indicator through which the lighting failure is known.
The operation of the prior art lighting failure detector depends upon the light detected by the photocell. The disadvantage of the photocell is that it deteriorates under ultraviolet and heat radiating from the lamps. As a result, the prior art lighting failure detector is likely to malfunction and cannot endure a long period of use.